This invention relates to electrical generators, and, more particularly, to stator core-end structures for reducing electromagnetic losses and associated heating in generator core-ends by using amorphous metal laminates.
The operating efficiency of electrical generators can be severely impacted by electromagnetic losses in the generator core-ends. More specifically, the axial component of magnetic flux normal to the plane of the generator stator core-end induces eddy currents in the stator core-end laminations. The eddy currents cause power loss and stator core-end region heating thereby limiting generator capacity due to thermal limits imposed by internal design guides and industry standards.
A typically constructed generator is shown in FIG. 1, to comprise stator 12, rotor 14, and armature end winding 36. Outside space block 32, stator flange 28 and key bar 30 maintain metal lamination packages 40 in place. Several ways have been proposed to reduce the electromagnetic flux normal to the stator core-end to minimize the eddy current losses and heating. For example, it has been proposed to increase the air gap 38 length towards the end of the stator core-end to reduce the detrimental effects of the electromagnetic flux. Core-end stepping 34 has also been proposed, as shown in FIG. 1, for eliminating or at least reducing the negative effects of the electromagnetic flux. And finally, it has also been proposed to reduce the relative axial length of the rotor with respect to the stator to minimize the core-end electromagnetic flux.
All of the above described actions, for reducing electromagnetic flux at the stator core-end of an electrical generator, have proven to be somewhat deficient in that in each case the generator requires an increased excitation which contributes to lower machine operating efficiency and a potentially bigger thermal problem.
Amorphous magnetic materials have the distinct advantage of having greatly reduced hysteresis losses. The core loss of amorphous metals, for example, is considerably lower than that of grain-oriented silicon steel. Furthermore, amorphous metal cores are able to respond to changes in a magnetic field much more quickly than conventional ferrous core materials. For all of these reasons, amorphous metals are an attractive substitute for silicon steel laminations, especially in the stator core-end to reduce loss and decrease core-end temperatures.
In an exemplary embodiment of the invention, a stator core-end construction comprises amorphous metal laminates which may be stepped to further reduce core-end losses. This construction has distinct advantages over the prior art in that the reduction of eddy currents and heating of the stator core-end is accomplished without any sacrifice of performance or machine efficiency. As a result, the present invention has application in newly constructed electric generators and for up-rating existing electric generators to achieve higher capacities.